refactor(pxe): migrate RecipientTaggingStore to BaseStagingStore (backport of aztec-labs-eng/aztec-node#94)

[nventuro]

Backport of aztec-labs-eng/aztec-node#94 to the v5 line: a git cherry-pick -x of its squash commit on aztec-node/main, 1f14e9a69d10d12177032cc3fa5acddbeea2b751. The change itself was described and reviewed there; this PR is only about the port being faithful, so please review it as such.

Validating the backport

1. Fetch the source repo once: git remote add node https://github.com/aztec-labs-eng/aztec-node && git fetch node main.

2. Compare the upstream patch with this PR's patch (range-diff compares patches, so unrelated histories are fine):

   git range-diff 1f14e9a69d^..1f14e9a69d origin/nico/port-node-94-recipient-tagging-store^..origin/nico/port-node-94-recipient-tagging-store
   

   Expected: only the (cherry picked from commit …) trailer under the commit message and nothing else — no -/+ lines under any file header. The patch applied without conflicts and was not edited.

3. Build and run the unit suites at this commit (from yarn-project/): yarn workspace @aztec/pxe build && yarn workspace @aztec/txe build && yarn workspace @aztec/pxe test && yarn workspace @aztec/txe test. The upstream PR's own tests are part of these suites, so passing them is the behavioral check; CI on this PR runs them as well.

Stack

Stacked on the backport of aztec-labs-eng/aztec-node#47 (base branch nico/port-node-47-base-staging-store); to be rebased onto merge-train/fairies-v5 once that one merges. Order: #20 → #35 → #40 → #47 → #94 → #100 → #98 (aztec-node numbers).